With the advent of the Internet and advancements in computer systems, online accounts have become an important part of our daily lives. Online accounts facilitate interactions between service providers and users (or customers) from anywhere in the world at any time. Because of these features, online accounts offer an unsurpassed level of convenience for the users. However, as online accounts have become popular, computer systems are facing new challenges that did not exist in the pre-Internet era. For example, in the pre-Internet era, physical access to computer systems was necessary for any unauthorized access to the networks supported by the systems. Because maintaining the security of a hosting facility was relatively easy, these systems and networks enjoyed a high level of security and isolation against unauthorized access.
However, the Internet has made it possible to access these systems from almost anywhere in the world. As a result, physical access to computer systems are not necessary anymore to manipulate or exploit the content of these systems. Therefore, new groups of sophisticated criminals, many of whom live outside the jurisdiction of the law enforcement of this country, have become active. Oftentimes, these criminals orchestrate attacks on the computer networks of major companies and steal valuable information. In many cases, the attackers gain access to the networks by obtaining the usernames and passwords of unsuspecting users. Thus, maintaining the security of online accounts has become an utmost important task for administrators of computer networks.